This invention relates to a packet-based telephony network and more particularly to a proxy system that negotiates codec schemes between different telephony systems in the telephony network.
Packet based networks digitize audio signals and convert the digitized signals into data packets. A telephony system connected to the packet based network groups voice samples that may or may not be compressed together into the data packets. The data packets are encoded and then encapsulated with a header that includes a destination address. The encapsulated data packets are sent to another telephony system in the packet based network associated with the destination address. Upon reception by the destination telephony system, the data packets are reassembled into the original voice sample stream decoded and output to a listener.
Signaling primitives must be interpreted and possibly converted between the different telephony systems in the telephony network. The encoding characteristics of each telephony system endpoint, such as voice compression, packet size, and voice/video capabilities, must be determined between the different telephony systems in order to establish a media connection over the packet based network. There are many different types of packet telephony systems with different encoding characteristics, both standard and proprietary. This makes it likely that the encoding scheme used by a telephony system originating a telephone call may not be compatible with the encoding scheme used by the telephony system at the call destination. If encoding schemes are not compatible, a telephone call cannot be established.
Efforts have been made within communication standards to use a lowest common denominator voice codec within any one packet telephony standard. However, telephony systems may employ different communication standards that do not communicate with each other. For example, opposite endpoints for a telephone call may use the same compression encoding technique, but use different telephony capability exchange protocols. If the telephony capability exchange protocols used by the two endpoints are incompatible, a call cannot be completed.
Accordingly, a need remains for ensuring the establishment of calls between different telephony systems in a packet based network.
Voice packets are redirected in packet telephony systems to a codec proxy system that makes voice endpoints involved in an end-to-end call appear to be using the voice codec required of it by the other endpoint, even if the endpoints do not possess the required codec capability. The codec proxy system acts as a broker during initial capability negotiations, and as a real-time transcoding facility between disparate codec capabilities once voice traffic begins. The resulting system allows non-standard, cost-optimized and feature specific packet voice endpoints to interoperate in a standards-based network. Processing resources that already reside in a packet based network, (e.g., routing and signal processing engines) are used as a platform for the codec proxy system. No new hardware facilities are, therefore, necessarily required to implement the proxy system.
A capability exchange broker in the codec proxy system determines how codecs on different endpoints of the telephone call are transcoded and returns capability exchange responses required by the signaling telephony system. The codec proxy system then determines the codec schemes that need to be used by the two packet telephony systems for establishing and conducting the telephone call. The codec information determined by the proxy system is then relayed to the two endpoints. If no compatible codec scheme exists between the two endpoints, a packet transcoder and rebuffering circuit provides the real-time packet-to-packet conversion from one codec scheme to another as determined by the capability exchange broker.
The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention, which proceeds with reference to the accompanying drawings.